Museo Galileo
italiano
Virtual Museum
Multimedia
Frictional electrostatic machine
Video   Text

 

From the mid-eighteenth century onward, one of the most common types of electrostatic machine was the plate model, which remained in use until the early twentieth century, at least for demonstration and teaching purposes.

Despite differences in shape and construction details, these machines displayed a set of common features: a disk, typically of glass, revolving on an axis fitted with a handle; one or more pairs of small leather cushions stuffed with horsehair or felt to rub the disk; and a pair of combs. These served to transfer the electric charges from the disk to the prime conductor, consisting of one or more hollow brass cylinders on which the charges accumulated.

When the disk is rotated, it is rubbed by the cushions, which charges the glass with positive electricity. Through electrostatic induction, the comb tips accumulate the negative charges, which tend to neutralize the positive charges on the glass. In this manner, the metal conductors to which the combs are connected become positively charged. By placing a grounded electrode near the combs, one can trigger a powerful spark, which instantly discharges the machine.

Globe and cylinder electrostatic generators, despite their different shapes, function in exactly the same manner.

Objects
Cylinder electrical machine

Cylinder electrical machine

Inv. 2739
Edward Nairne, London, ca. 1778

Cylinder electrical machine

Cylinder electrical machine

Inv. 392
George Adams junior, London, late 18th cent.

Drum electrical machine

Drum electrical machine

Inv. 3408
Maker unknown, ca. 1776

Globe electrical machine, Nollet type

Globe electrical machine, Nollet type

Inv. 1341, 1342, 2737
Museo di fisica workshops, ca. 1775

Kundt and Cantoni electrical machine

Kundt and Cantoni electrical machine

Inv. 507
Maker unknown, ca. 1870

Modified Carré electrical machine

Modified Carré electrical machine

Dep. LV, Torino
Maker unknown, Turin, ca. 1890

Nairne cylinder electrical machine

Nairne cylinder electrical machine

Inv. 2736
Edward Nairne, London, 1773

Plate electrical machine

Plate electrical machine

Dep. LV, Torino
Maker unknown, early 19th cent.

Plate electrical machine

Plate electrical machine

Inv. 3766
Maker unknown, second half 18th cent.

Plate electrical machine

Plate electrical machine

Inv. 3909
Maker unknown, second quarter 19th cent.

Plate electrical machine

Plate electrical machine

Inv. 2705
Maker unknown, English?, second half 18th cent.

Portable globe electrical machine

Portable globe electrical machine

Inv. 444
Edward Nairne, London, ca. 1770

Portable globe electrical machine

Portable globe electrical machine

Inv. 516
Maker unknown, late 18th cent.

Portable plate electrical machine

Portable plate electrical machine

Inv. 2686
Maker unknown, ca. 1775

Portable plate electrical machine

Portable plate electrical machine

Inv. 2688
Maker unknown, English?, ca. 1775

Portable plate electrical machine

Portable plate electrical machine

Inv. 374
Maker unknown, second half 18th cent.

Portable plate electrical machine

Portable plate electrical machine

Inv. 2689
Maker unknown, English?, ca. 1775

Portable plate electrical machine

Portable plate electrical machine

Inv. 2687
Maker unknown, English?, ca. 1775

Winter plate electrical machine

Winter plate electrical machine

Inv. 1526
Museo di fisica workshops, second half 19th cent.